If a serious objection to one of Birmingham's – allegedly – ideologically infiltrated state schools is, according to a leaked report , its failure "properly to prepare pupils for life in modern Britain", the culprits find themselves, in throwback terms, in exalted company. Fellow suspects include the entire cast of the state opening of parliament, a host of judges, any number of Ukip candidates and, of course, the British aristocracy, whose most celebrated progressives, the Duke and Duchess of Cambridge, are now conditioning their infant son to accept as inevitable his future as defender of the faith.

True, with the obvious exception of Prince Charles, few of the above would probably feel more comfortable with an Islamic state, apparently another criticism of the "Trojan horse" suspect, but here, too, Birmingham academies are surely entitled to feel sore about Ofsted's objections to attitudes which, had they been advertised on a designated faith school's prospectus, might have looked respectable, even admirable.

It is difficult, for example, to conceive of a school more openly rejecting of Britain's predominantly secular culture than the Cardinal Vaughan comprehensive in Kensington, London, where 99.7% of the pupils are Catholic, the principal activity is "the apostolic mission of the Church" and "the teachings of Christ permeate all areas" – unless it is the Yesodey Hatorah Senior girls' school, a state-funded institution serving the Orthodox Jewish Charedi community in Stamford Hill in London. An Ofsted inspection in 2006 noted: "The Charedi community do not have access to television, the internet or other media. All members of the community aim to lead modest lives governed by the codes of Torah observance." It was marked grade one, "an outstandingly effective school".

Supposing the Charedi set-up should therefore appeal more widely, in the same way that outstanding Anglican schools have reached out to formerly godless politicians, the school website makes clear (as far as is practicable in the prohibited, online format) that its voluntary-aided status entitles the governors to keep out atheists and incompatibles, staff as well as pupils. Although some state-funded faith schools must now let in a fixed quota of infidels, to the fury of Catholics who, nowadays, prefer preaching to the converted, Yesodey is legally entitled, despite being funded by taxpayers, to discriminate against virtually all its benefactors. Parents will need a signed form confirming their commitment to the faith and, as for the girls, "any disputes as to whether a child is Jewish will be settled by reference to the Rabbinate of the Union of Hebrew Congregations".

And yet there are still a few chinks through which the outside world might seep and contaminate children who, if this part of the state system works perfectly, should emerge, aged 18, fully equipped for a lifetime's religious segregation and with the familiarity with modern British life of the average Martian. Even with the most tactful phrasing, public examinations have the potential to conjure up the existence of another world, one tainted by fossils as well as homosexual marriage. One solution, attempted last year by Yesodey Hatorah, is to redact exam questions featuring, say, the evolution of species. Ofsted's response, surely mild in the circumstances, was to say: "If Ofsted believed any school was deliberately preventing children from receiving a broad and balanced curriculum, this would be taken very seriously."

In practice, with the blessing of both Labour and coalition governments, each with its own influential complement of religious fanatics, the most devout faith schools are explicitly dedicated to that very task, thereby ensuring that, say, young earth creationists are not troubled by conflicting worldviews featuring the big bang, Lord Brahma, the possibility of premarital sex minus damnation. In the face of public hostility , protests by prominent scientists , galloping secularism, allegations of abuse and the routine exclusion of children from nearby schools for sectarian reasons, successive education ministers have cultivated a system that, even before the recent growth of faith schools, was acknowledged as a major cause of social segregation . Labour's Tristram Hunt, though he virtuously objects to any "narrowing of the curriculum" in religious schools, appears to have no problem with their actual existence, as though divinely ordained hostility towards homosexuality could, if they toned the bigotry down a bit, somehow be made compatible with the existence, in every school, of children destined to define as LGBT.

In fact, recent criticism of Ofsted inspectors for tactlessly mentioning gay people, of whom some Muslim pupils were apparently being kept unaware, should be set against that body's advice that inspectors screen themselves as relentlessly for traces of secular attitudes before entering a faith school as they might, say, check for botulism. "Boys and girls may be seated separately", it advises, of Muslim schools. "This should not be taken as a sign of inequality between different genders." Female Ofsted inspectors are urged – although this should not be taken as a sign of inequality between different genders – to abandon their traditional swimsuits in favour of "a trouser suit or longer skirt and jacket to cover their arms".

In Jewish schools (most dress hints are aimed at women inspectors) they should avoid trousers, ditto bright colours "and red in particular", presumably to avoid distressing pupils hitherto protected from modern polychromicity. In some Muslim schools, it adds – not that this should be taken as a sign of inequality between different genders – "male inspectors will need another female present in order to give feedback to a female teacher". All of which would be second nature to any of the religious specialists from the Bridge Schools Inspectorate, promoted by both Muslim and Christian campaigners and now employed by the DfE.

Mercifully, perhaps, the religious part – section 48 – of a faith school inspection is invariably devolved to fellow believers, likely to respond eagerly to copious worship or any promising signs of irreversible indoctrination, ditto marginalisation. "The House system now has patron saints," writes one Catholic enthusiast of an innovation that would not, one imagines, be applauded by evangelicals. At Grey Coat in Westminster, Mr Gove's favourite, the inspector congratulated students "able to identify the contribution of a number of scholars to the Design argument for the existence of God". It was noted at Cardinal Vaughan, "where pupils were studying the Catholic response to abortion, learning was organised very effectively, so that pupils could develop sophisticated reasons to support the Catholic view".

No doubt this will seem unfair to state schools that find themselves condemned for practices that would earn them high praise from an approved, culturally isolationist inspector, and minus the immunity from secular legislation that has long facilitated the suppression in officially pious establishments of heretics, scientists and homosexuals.

The big mistake of Operation Trojan horse, if it ever existed, was to go to all that trouble when, following a straightforward application to the secretary of state, its owners could have plonked the quadruped down in plain sight, called it a faith school, and got on with doing God's will.